In an image forming apparatus for forming images by use of toner, such as a printer, a copying machine, and a facsimile, it is necessary to grasp the amount of remaining toner for convenience of maintenance such as toner supply.
However, in a case where an image forming apparatus is provided with a remaining toner detection device, the cost inevitably increases. Therefore, there has been used a technique in which the amount of remaining toner is detected by use of existing members.
For example, Japanese Unexamined Patent
Publication No. 221944/1998 (Tokukai 10-221944; published on Aug. 21, 1998) discloses a technique in which: when two-component developer is used, the amount of remaining toner is detected based on the result of Auto Toner Control (ATC).
ATC is a method for controlling toner density of developer so that the toner density is constant based on magnetic permeability of the developer. Two-component developer is constituted of (i) carrier made of iron powder and the like and (ii) toner with predetermined density (e.g. 4 to 5%). As such, when toner in the developer is used and the ratio of carrier increases, the magnetic permeability of the developer increases. Therefore, by detecting the magnetic permeability of the developer, it is possible to grasp the ratio of toner in the developer.
Examples of ATC include (i) a technique in which: when magnetic permeability rises and exceeds an upper limit (corresponding to a lower limit of toner density), a supply motor is rotated for a predetermined time (alternatively, predetermined number of rotations) and toner is supplied from a toner supply source such as a toner bottle, and (ii) a technique in which: a lower limit of magnetic permeability (corresponding to an upper limit of toner density) is previously set and when the magnetic permeability rises and exceeds an upper limit, a supply motor is rotated until the magnetic permeability falls to the lower limit, thereby supplying toner from the toner supply source.
In either technique, as the amount of remaining toner in the toner supply source drops, the effect of drop appears in ATC. The result of ATC allows detection of the amount of remaining toner. Namely, in the technique (i), the amount of toner supply per a predetermined time for rotating the supply motor is reduced, so that toner supply is frequently repeated, which makes it possible to detect that the amount of remaining toner is small. Further, in the technique (ii), the amount of toner supply per a predetermined time for rotating the supply motor is reduced, so that the time for toner supply (time taken for the magnetic permeability to fall to the lower limit) becomes long, which makes it possible to detect that the amount of remaining toner is small.
Thereafter, when the supply motor is rotated for a predetermined time (e.g. 3 seconds) but the magnetic permeability does not have the former value, namely, when the toner density does not increase, toner empty (toner run out, toner end) is detected.
Further, examples of a conventional technique for detecting the amount of consumed toner or remaining toner by use of existing members other than ATC are as follows.
Japanese Unexamined Patent Publication No. 163553/2004 (Tokukai 2004-163553; published on Jun. 10, 2004) discloses a technique in which: the number of formed printing dots is counted, the counted number is multiplied by a predetermined weight coefficient, thus multiplied number is accumulated and, based on thus accumulated number, the amount of toner consumption is obtained. Further, Japanese Unexamined Patent Publication No. 163553/2004 discloses that the weight coefficient is modified according to the history of toner use.
Further, Japanese Unexamined Patent Publication No. 163554/2004 (Tokukai 2004-163554; published on Jun. 10, 2004) discloses a technique in which the amount of remaining toner is obtained in such a manner that (i) the number of printing dots is counted based on image signals and the amount of toner consumption is calculated based on the counted number, and (ii) in an operation mode such as a density control mode which includes formation of a patchwork image, the amount of toner consumption is calculated according to a pattern of the patchwork image.
Further, Japanese Unexamined Patent Publication No. 333419/1998 (Tokukaihei 10-333419; published on Dec. 18, 1998) discloses a technique in which: a toner supply function for converting a video count value of an image in to a time for toner supply is corrected while being weighted by a video count value of an image under formation, and thus the amount of toner supply is corrected so as to correspond to the amount of toner consumption.
However, the conventional techniques for detecting the amount of remaining toner by use of existing members have the following problems to be solved.
For example, in the technique disclosed in Japanese Unexamined Patent Publication No. 221944/1998 for detecting the amount of remaining toner by carrying out ATC, it is impossible to chronologically detect the amount of remaining toner from a time when the toner is fully contained to a time when the toner runs out. Hence there is not an enough time for a user to prepare toner to be subsequently used, so that the operation rate of the image forming apparatus drops.
Namely, in ATC, it is not until the amount of remaining toner is much reduced that toner supply is frequently repeated or that it takes much time to supply toner per each supply. When the amount of remaining toner is much reduced, the number of printable sheets is only 50 to 100 (the number depends on the size of a sheet and a printing ratio). As a result, though a user is informed that the amount of remaining toner is small at a time when such state is detected, it is much likely that the toner runs out before next toner is prepared, resulting in that the image forming apparatus is stopped.
On the other hand, in the techniques not using ATC, disclosed in Japanese Unexamined Patent Publication No. 163553/2004, Japanese Unexamined Patent Publication No. 163554/2004, and Japanese Unexamined Patent Publication No. 333419/1998, the amount of toner to be used is exactly calculated based on image signals or patterns of patchwork images, and is regarded as the amount of toner consumption. Therefore, by obtaining the amount of remaining toner based on thus obtained amount of toner consumption, it is possible to detect that the amount of remaining toner is small before ATC does so that the detection result is informed to the user.
However, the actual amount of toner on a photoconductor is not constant because of the environment or variations in devices. Therefore, even though the amount of remaining toner is more exactly detected based on weighting or the like, it is difficult to determine whether toner runs out or not based only on the result of weighting.
Therefore, even though the user is informed that the amount of remaining toner is small under a condition that enough sheets are provided so as to be printed, toner may run out before a predetermined number of sheets are printed or toner may be judged to run out while the toner still remains.